An API (application programming interface) basically allows an application to communicate with other applications. Without realizing it, we are all using APIs. If you are surfing the web and using a mobile phone, then you are using APIs without necessarily being aware of it.

Some practical examples:
In many web services, as soon as we see a map, it is from Google Maps. To provide this map, the service uses Google Maps’ API, with just a few simple lines of code.
When you click a ‘Facebook like’ button in an application or on a website, or when you view Facebook content on a Web page, you are using the Facebook API. APIs allow Facebook to broadcast its service on 1,000 new sites per day, and it would be impossible for their teams to do it manually.

Your service, product or application needs APIs:
– To access technical resources quickly and cheaply (imagine what adding maps to your website would cost; nobody can afford to redo Google Maps);
– Because most large IT service providers offer their services in the form of APIs;
– And because it is sometimes the only way to access some companies’ services.